XML 140 R105.htm IDEA: XBRL DOCUMENT
v2.4.0.8

Fair value - pension level 3 (Details 10) (Corporate debt securities [Member], Fair value, measurements using significant unobservable inputs (Level 3), Pension Benefits, USD $) In Thousands, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2012
Corporate debt securities [Member] | Fair value, measurements using significant unobservable inputs (Level 3) | Pension Benefits |
Defined Benefit Plan Disclosure [Line Items] |
Balance at beginning of year | $ 289
Total realized/unrealized losses | (47)
Purchases, issuances and settlements (net) | (242)
Balance at end of year | $ 0

X
- Definition Fair value measurement with unobservable inputs reconciliation recurring basis realized and unrealized gains losses. + References No definition available. + Details
Name: | mdu_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisRealizedAndUnrealizedGainsLosses
Namespace Prefix: | mdu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of purchases, (sales), issuances and (settlements) of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph c -URI http://asc.fasb.org/extlink&oid=25499696&loc=d3e19207-110258 + Details
Name: | us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchasesSalesIssuancesSettlements
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=25499696&loc=d3e19207-110258 + Details
Name: | us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant